Internal combustion engines have a cylinder block with a cylinder head mounted thereon. The block and cylinder head have mounting surfaces with a cylinder head gasket in between and the two are coupled together by threaded bolts. The cylinder block has multiple cylinders each having a piston which reciprocates therein. A combustion chamber is delimited by the cylinder head, cylinder walls, and the piston.
Intake ports through which the fresh mixture is supplied to the combustion chamber and exhaust ports through which the exhaust gases are removed from the combustion chamber are provided in the cylinder head. A valvetrain actuates the intake and exhaust valves which cover the intake and exhaust ports, respectively. Each cylinder has at least one each of an intake and an exhaust valve. Many engines have multiple intake valves and multiple exhaust valves per cylinder to provide additional cross-sectional area through which gases can flow to improve scavenging.
The exhaust exiting the engine may be fed to a turbine of an exhaust turbocharger and/or exhaust gas aftertreatment devices. To ensure that the exhaust gases entering the turbocharger and/or aftertreatment devices are hot, to achieve a rapid lightoff of the aftertreatment devices, and to reduce turbocharger lag, it is desirable to mount the turbocharger and/or aftertreatment devices close to the location that the exhaust gases exit the combustion chamber.
A cylinder head with an integrated exhaust manifold and with liquid cooling is disclosed, for example, in EP 1 722 090 A2 in which a compact cylinder head is provided. The cooling of the cylinder head described in EP 1 722 090 A2 proved to be inadequate in practice due to thermal loading in the region where the exhaust gas ducts converge into the overall exhaust duct. To prevent melting, the fuel/air mixture is enriched whenever high exhaust gas temperatures are expected, which results in more fuel being injected than can by burned by the air quantity provided, thus a penalty in fuel economy.